In order to provide a more compact format for identifying mixtures of refrigerants in the following discussions, mixtures of refrigerants will be listed in the form of:
R-ABC/DEF/GHI (N0/N1/N2) or PA1 R-ABC/DEF/GHI (N0-N0'/N1-N1'/N2-N2')
which is a mixture of refrigerants (fluids) R-ABC, R-DEF, and R-GHI where N0, N1, and N2 are the weight percentages of each component fluid. The second form is similar, but specifies ranges of weight percentages of each of the component fluids, with the total being 100 percent. For this application, the following Table 1 discloses relevant single refrigerant R-numbers with their chemical names.
TABLE 1 ______________________________________ R-number Chemical name ______________________________________ R-134a 1,1,1,2-tetrafluoroethane R-134 1,1,2,2-tetrafluoroethane R-600a isobutane (i-C4H10) R-152a 1,1-difluoroethane R-227ea 1,1,1,2,3,3,3-heptafluoropropane R-125 pentafluoroethane R-142b 1-chloro-1,1-difluoroethane R-124 2-chloro-1,1,1,2-tetrafluoroethane R-22 chlorodifluoromethane R-12 dichlorodifluoromethane ______________________________________
The automotive industry has switched away from the environmentally damaging refrigerant dichlorodifluoromethane (R-12) to 1,1,1,2-tetrafluoroethane (R-134a), beginning with the 1994 model year. Nearly all pre-1994 cars that were retrofitted from R-12 to R-134a refrigerant systems have had cooling performance problems. The 1994 and later model year cars were manufactured with R-134a refrigerant systems, in general. Some have performed well, and some have not. R-12 refrigeration systems used 500-viscosity mineral oil as a compressor lubricant. R-134a does not dissolve in (is not miscible with) mineral oil, so the mineral oil will not return to the compressor properly. New refrigeration systems lubricants were developed for R-134a, which were primarily polyalkylene glycol (PAG) based oils and polyol ester (POE) oils. The bulk of 1999 model year cars contain PAG oils. Chlorinated refrigerants, such as R-406A (R-600a/R-22/R-142b (4/55/41)) (see also U.S. Pat. No. 5,151,207) or R-12, cannot be directly used in systems that use PAG oils as almost all PAG oils are destroyed by chlorinated refrigerants. Only nonchlorinated components may be used in creating an R-134a substitute to avoid destruction of the PAG oil. However, a recently developed PAG oil, brand name Daphne.RTM. of Idemitsu Kosan Kabushiki, Tokyo, Japan (also known as "double end capped PAG oil"), has claimed to be able to tolerate chlorides and has even claimed to be able to run in R-12 systems without breakdown. This oil is not in widespread use at this time. Millions of cars have been and continue to be manufactured using the original, chloride sensitive PAG oils.
One option to improve the performance of a poorly performing R-134a refrigerant system is to painstakingly remove all the PAG oil by disassembling and flushing the system, including the compressor. Mineral oil can then be charged into the system along with R-406A, R-12 or any other blend refrigerant that offers a performance improvement over the performance of R-134a. This process is very labor intensive.
My currently co-pending U.S. patent application Ser. No. 08/820,843, filed Mar. 20, 1997, discloses several refrigerant mixtures for R-134a systems that can offer significant performance improvements over R-134a. These mixtures are zeotropic blends that create a "glide" or temperature range over which condensation and evaporation take place, increasing utilization of the condenser at rejecting heat and the evaporator at gaining heat. The optimum glide is in the range of 15-20.degree. F. For optimum performance, one needs to bracket the boiling point of R-134a across it's normal operating range with a refrigerant blend comprised of components that boil above and below R-134a's boiling point in order to create the necessary glide. The refrigerant mixture disclosed in co-pending U.S. patent application Ser. No. 08/820,843 have created as much as a 10-12.degree. F. lowering of air conditioning duct temperatures in real vehicles over that achieved with R-134a, alone.
R-134a boils at -14.8.degree. F. at 1 atmosphere pressure. Suitable "high boilers" (around 0-+10.degree. F.) are either very flammable (isobutane) or very expensive (R-227ea), or are not made in production quantities (R-134) (not to be confused with the R-134a isomer, which is massively produced).
A mixture disclosed in my co-pending U.S. patent application Ser. No. 08/820,843, sold under the trade name GHG-X7, comprised of R-227ea/152a/125 (55/5/40), has been used in R-134a automotive air conditioning systems for over two years with excellent results. Cold air supply duct temperatures are often in the 40.degree. F. range compared to the mid to high 50.degree. F. duct temperatures for R-134a. However, the R-227ea component is very expensive. It currently retails for about US$20 dollars per pound.
Hydrocarbon refrigerants (100% hydrocarbons) can be blended to replace R-134a, and these blends are compatible with PAG or POE oils (POE may thin out too much). A typical blend would be 60/40 by weight of propane/isobutane. These blends are highly flammable and are banned in about 18 states at the present time.
Another blend, R-414B, is claimed by its manufacturer to replace R-134a without regard to the type of oil present. R-414B is comprised of R-22/124/600a/142b (50/39/1.5/9.5). All components of R-414B, except the R-600a, are chlorinated fluids that can be expected to destroy the most common PAG oils used in automotive compressors. About 15 ml of R-414B was added to a 5 ml sample of GM part 1#15-118 PAG refrigerant oil for R-134a systems. The oil darkened overnight, and turned black by the fourth day.
No other prior art is known for specifically replacing R-134a in poor performing applications.